In 3d modeling, these are modular assemblies of small detail models applied to the surface of larger models to add visual interest/complexity to otherwise plain areas. The detail models are generally designed to look like they serve some sort of mechanical/technological function, although what said function is specifically is typically ambiguous.

The term dates back to at least the 1970s, when it was used among cinematic special effects artists to refer to physical models used in the same way in the construction of props and miniatures. At that time, they were often made from kitbashed hobby models of battleships, tanks, and cars.

Today, the term usually refers to digital 3d models of this nature, which are created in the same manner as any other 3d model, but reused repeatedly to speed up the process of creating subsequent models.

It can also be used as a verb to describe the act of applying nurnies.